The present invention pertains to the vacuum tube art, particularly getter materials for maintaining vacuums. It finds particular application in conjunction with rotating anode x-ray tubes for CT scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also find application in conjunction with other vacuum tubes for the generation of radiation and vacuum tubes for other applications.
Typically, rotating anode x-ray tubes include a sealed and evacuated envelope in which the cathode, anode, anode bearings, anode rotor, and other associated structures are sealed. Because the envelope is evacuated, getter material is usually provided inside the envelope to maintain the vacuum state. The getter material binds gases on its surface and/or absorbs such gases to maintain the vacuum state in the tube after it has been exhausted. This process of removing residual gases from an evacuated area by binding and/or absorbing is known as pumping.
A getter shield is also provided to the x-ray tube at an end of the tube opposite the anode to protect the getter and encase selected electronics of the tube. Getter shields are typically constructed of 1215 steel.
With respect to the getter material itself, some prior systems have utilized a barium wire getter mounted within the getter shield. Other prior systems have used a porous getter in contact with a resistance heater enclosed in a ceramic package. The porous getter was mounted within the getter shield and heated by passing electric current through the resistance heater. Still other prior systems utilized a porous getter attached to wire mounted legs with a ceramic material in a cartridge. The cartridge was mounted within the getter shield. Heat was provided to the getter by thermoradiation from the target striking the getter by passing through holes drilled through the getter shield.
These prior systems have had difficulties. First, insufficient getter material is provided to maintain desired pumping speed and gas capacity. Second, prior getter materials have undesirably long activation times requiring high temperatures and low pressure. Last, the prior systems achieve relatively low temperature levels which compromise operation.
The present invention contemplates a new and improved x-ray tube using a getter shield and method which resolves the above-referenced difficulties and others.